Belt charging means for borehole electrostatic generators



5 POWER March 6, 1962 R. A. BERGAN ET AL 3,024,407

BELT CHARGING MEANS FOR BOREHOLE ELECTROSTATIC GENERATORS Filed Aug. 20,1959 2 Sheets-Sheet 1 LOAD 59 1 7, E j Eva} 5e- 7s 1 6 I 8 1 1 62 a I jl 70 1 72 POWER 3% I i SUPPLY 1 IN V EN TORS REUBEN A. BERGAN 8 ARTHURH. YOUMANS ATTORNEY March 6,, 1962 Filed Aug. 20, 1959 LOAD POWER SUPPLYR. A- BERGAN ET AL BELT CHARGING MEANS FOR BOREHOLE ELECTROSTATICGENERATORS 2 SheetsSheet 2 CD 20 227 8 Isa f;

POWER SUPPLY REUBEN A. BERGAN & ARTHUR H. YOUMANS AT TORNEY IN VEN TORSnited States Patent ()fiice 3,024,407 Patented Mar. 6, 1962 3,024,407BELT CHARGING MEANS FOR BOREHOLE ELECTROSTATIC GENERATORS Reuben A.Bergan and Arthur H. Youmans, Tulsa, Okla, assignors to Well SurveysIncorporated, a corporation of Delaware Filed Aug. 20, 1959, Ser. No.835,029 7 Claims. (Cl. 322-2) This invention relates to belt-typeelectrostatic generators and particularly to novel methods and apparatusfor charging the belt of a belt-type electrostatic generator.

In a belt-type electrostatic generator, such as a Van de Graatfgenerator, an electrically insulating belt is driven about a pair ofspaced pulleys. Electrical charges of one polarity are applied to thebelt adjacent one pulley. Adjacent the other pulley, the charges areremoved from the belt at a point within a high voltage terminal wherethey are accumulated to develop and maintain the required high voltage.The charge per unit time which can be carried by the belt to the highvoltage terminal is dependent upon a number of variables. However, forany particular belt, at a particular linear velocity, and under a givenset of conditions, a maximum charging rate exists. Should one wish toincrease the charging rate beyond this point, it has been found that thecharging rate can be substantially doubled by making the belt carrycharges of one polarity to the high voltage terminal on its upwardtravel and carry charges of the opposite polarity away from the highvoltage terminal on its downward travel. In order to accomplish this, itis necessary to provide some means inside of the high voltage terminalnot only for removing charges of one polarity from the belt, but alsoapplying charges of the other polarity to the belt for transport toground potential.

Particularly because of severe space limitations, this problem isespecially acute in electrostatic generators which are intended for usein subsurface instruments, such as those employed in nuclear welllogging. Such borehole generators have been limited to the chargingrates obtainable when only the upward travel of the belt is charged. Atthe same time, the power available to energize borehole generators isgreatly restricted by such problems as transmission over the supportingcable which may be several miles long, borehole temperatures which maybe as high as 400 degrees Fahrenheit, and portability of the loggingapparatus. Consequently, the added efficiency obtainable by charging thedownward travel of the belt is sorely needed in borehole generators.

These disadvantages of the prior art are overcome with the presentinvention and novel means are provided for charging the downward travelof the belt of an electrostatic generator in a regulated manner and forindependently controlling the charging of the downward travel of thebelt. Moreover, the apparatus of the present invention is sufficientlycompact to permit its use in borehole electrostatic generators.

The advantages of the present invention are preferably attained bydeveloping a potential difference across a voltage dropping device, suchas a resistor, vacuum tube or corona gap, within the high voltageterminal of a belt-type electrostatic generator and connecting theopposite sides of the voltage dropping device to suitable electrodes toinduce a charge of appropriate polarity on the downward travel of thebelt. This can easily be accomplished, the inventors have discovered,even in the limited space available in a bore hole generator and permitsregulated charging of the downward travel of the belt. As noted above,such charging of the downward travel of the belt substantially doublesthe charging current capacity of belt-type electrostatic generators. Inparticular, in those instances where the generator is employed toenergize an ion acceleration tube, as in a borehole acceleratorneutron'source, the voltage drop across the ion source of theacceleration tube may be employed as the voltage dropping device. Thispermits charging of the downward travel of the belt to be convenientlycontrolled by controlling the gas pressure in the acceleration tube.

Accordingly, it is an object of the present invention to provide novelmeans for charging the belt of a belttype electrostatic generator.

Another object of the present invention is to provide novel means forapplying a regulated charge to the downward travel of the belt of abelt-type electrostatic generator.

A further object of the present invention is to provide novel means forcharging the belt of a belt-type electrostatic generator which means issufliciently compact to permit its use in borehole generators.

An additional object of the present invention is to provide novelmethods and apparatus for controlling the charging of the downwardtravel of the belt of a belttype electrostatic generator.

A specific object of the present invention is to provide novel means forcharging the belt of a belt-type electrostatic generator, said meanscomprising a voltage dropping device located within the high voltageelectrode of said generator, means developing a potential differenceacross said voltage dropping device, and means connecting the oppositesides of said voltage dropping device to suitable electrodes to induce acharge on the downward travel of the belt of said generator.

These and other objects and features of the present invention will beapparent from the following detailed description wherein reference ismade to the figures of the accompanying drawings.

In the drawings:

FIG. 1 is a view, partly in section, of a typical belttype electrostaticgenerator embodying the present invention;

FIG. 2 is a view, partly in section, of the high voltage terminal of thegenerator of FIG. 1 embodying a modi fied form of the present invention;

FIG. 3 is a view, partly in section, of a modified form of the apparatusof FIG. 1; and

FIG. 4 is a View partly in section, of a further modified form of theapparatus of FIG. 1.

In those forms of the invention chosen for purposes of illustration inthe drawings, FIG. 1 shows a typical belt-type electrostatic generatorhaving a non-conductive belt 2 formed with conductive stripes normal tothe belt travel and located on the inside of the belt. The belt 2 isdriven by motor driven lower pulley 4 and passes about upper pulley 6mounted inside the high voltage terminal 8. Any of several conventionalmeans may be employed to charge the belt adjacent the lower pulley 4. Asshown, the lower pulley 4 is grounded by conductor 10 and charges areinduced on the belt 2 by induction plate 12 which is energized by asuitable power supply 14. Induction plate 12 may obviously be made toinduce either positive or negative charges on the belt 2. For the sakeof description, it is assumed that in this instance the charge inducedon the belt is positive, as indicated at 16 in FIG. 1. Grounding of thelower pulley 4 also serves to remove charges from the downward travel ofthe belt.

An idler pulley 18 engages the belt 2 inside of the high voltageterminal 20 and allows charges to flow from the belt 2 through conductor22 to the high voltage terminal 20. A second conductor 24 connects thehigh voltage terminal 20 to one side of a voltage dropping device 26,which is shown in FIG. 1 as a corona regulator tube, but which may be aresistor, vacuum tube or other suitable device. The other side of thevoltage dropping device is connected to a suitable load 28 by conductor30 and to the upper pulley 6 by conductor 32. Because of the potentialdrop across the voltage dropping device 26, the upper pulley 6 ismaintained at a lower potential than the high voltage electrode 20.Thus, by placing an induction plate 34 near the upper pulley 6 adjacentthe upper end of the downward travel of the belt 2 and connecting theinduction plate 34 to the high voltage electrode 20 by conductor 36, acharge may be induced on the downward travel of the belt 2, as indicatedat 38-. Upon reaching the lower pulley 4, these charges pass throughconductor to ground.

FIG. 2 illustrates a modified form of apparatus for charging thedownward travel of the belt of a belt-type electrostatic generator. Asin FIG. 1, the belt 2 is shown carrying a positive charge, indicated at16, during its upward travel and passing over an upper pulley 6 withinthe high voltage terminal 20. In this form of the invention, the chargecarried by the belt 2 during its upward travel is removed by the upperpulley 6 and passes through conductor 40 to the high voltage terminal20. At the upper end of the high voltage terminal are mounted a pair ofconcentric sleeves 42 and 44 which are isolated from each other, byinsulator 46, and from the high voltage terminal 20, by insulator 48. Apair of electrodes 50 and 52 are mounted above the sleeves 42 and 44 andare insulated from each other by insulator 54. Electrode 50 is the highvoltage electrode and is connected by conductor 56 to the high voltageterminal 20 to provide a high voltage for the load-s 5 8 and 59 whichare connected between electrode 50 and ground. Electrode 52 is thereturn or low voltage electrode for the load 58. As shown, electrode 52is isolated from sleeve 44 by insulator 60 but makes contact with sleeve42. A cylindrical tank 62 surrounds the generator assembly and coronapoints 64 and 66 are provided to establish predetermined voltage dropsbetween sleves 42 and 44 and between sleeve 44 and the tank 62 which isgrounded, as shown at 68.

It will be seen that in the apparatus of FIG. 2, sleeves 42 and 44 aremaintained at different potentials by reason of the corona gap formed bysleeve 42 and corona point 64 mounted on sleeve 44. This potentialdifference may be employed to induce charges on the downward travel ofthe belt 2. To accomplish this, an idler pulley 70 is positioned toengage the downward travel of the belt 2 adjacent, but separated from,the upper pulley 6. The idler pulley is connected to sleeve 44 byconductor 72. In addition, an induction plate 74 is mounted adjacent theidler pulley 70 on the opposite side of the downward travel of belt 2and is connected by conductor 76 to sleeve 42. Thus, idler pulley 70 andinduction plate 74 are maintained at the potentials of sleeves 44 and 42respectively and charges are induced on the downward travel of the belt2, as indicated at 38.

In those forms of the invention shown in FIGS. 1 and 2, it will be seenthat the charge applied to the downward travel of the belt depends onthe voltage difference between the induction plate and the adjacentpulley. Where the voltage dropping device 26 is a resistor, this willvary somewhat with the charge carried by the upward travel of the belt.Thus, the charging rate of the downward travel of the belt may be tosome extent controlled by controlling the charging rate of the upwardtravel of the belt. This may be accomplished in any convenient manner,such as those disclosed in the copending application of Eric C.Hopkinson, Serial No. 752,701, filed August 4, 1958, entitled ControlSystem for Artificial Sources of Radiation and Robert L. Tucker, SerialNo. 771,624, filed November 3, 1958, entitled Apparatus for RegulatingBelt-Type Electrostatic Generators. Moreover, the belt speed may becontrolled by varying the speed of the driving motor. This may beaccomplished in any convenient manner and many ways of controlling themotor speed are well known in the art. This also determines the rate atwhich charge is carried between the high voltage electrode and ground.

While these forms of the invention permit control of the charging of thebelt, it will be seen that in each form of the invention hereinabovedescribed the charging of the downward travel of the belt cannot becontrolled independently of the charging of the upward travel of thebelt. In some instances, it may be desirable to control the charging ofthe downward travel of the belt independently of the charging of theupward travel of the belt. This may be accomplished in several differentways, as hereinafter described. In each of the forms of the inventionshown in FIGS. 1 and 2, a potential difference is developed across asuitable voltage dropping device. While the voltage dropping device hasbeen shown for convenience in the drawings as comprising a corona gap,it has been noted that other voltage dropping devices, such as resistorsor vacuum tubes, may also be employed. Furthermore, if the voltagedropping device is variable, the charge applied to the downward travelof the belt may be controlled by varying the electrical impedance of thevotlage dropping device and such control will, obviously, be independentof the charging of the upward travel of the belt.

Charging of the downward travel of the belt may be controlledindependently of the charging of the upward travel of the belt byconnecting a variable resistance device in series between the lowvoltage side of the voltage dropping device and the electrode whichapplies the charge to the downward travel of the belt, as shown in FIG.3. The apparatus of FIG. 3 is substantially identical to that of FIG. 1and operates in a similar manner. However, a variable resistance 33 isconnected in conductor 32 between the low voltage side of the coronatube 26 and the upper pulley 6. The variable resistance 33 may be anysuitable device and may be controlled in any appropriate manner tocontrol the voltage applied to pulley 6.

In some instances, the potential drop across the load may be employed asthe variable resistance to control the charging of the downward travelof the belt independently of the charging of the upward travel of thebelt. An example of this type of control is shown in FIG. 4. Theapparatus of FIG. 4 is similar to that of FIG. 1. However, the load 28of FIG. 1 is shown in FIG. 4 as an ion source having an anode 35 andcathode 37, such as is employed in the acceleration tube 39 of anaccelerator-type neutron source for nuclear well logging instruments,such as disclosed in the patent to Arthur H. Youmans, Patent No.2,689,918, issued September 21, 1954. It has been found that theelectrical impedance between the anode 35 and cathode 37 is a functionof the gas pressure in the acceleration tube 39. Moreover, the gaspressure may be controlled by suitable means, such as pressure controlelement 41, as described in the copending application of Arthur H.Youmans, Serial No. 804,360, filed April 6, 1959, entitled Control ofPressure in a Static Atmosphere Ion Accelerator. Thus, by controllingthe pressure of the gas in the acceleration tube 39, the potentialbetween the anode 35 and cathode '37 of the ion source may be regulated.This variable potential serves as a variable resistance to control thecurrent in conductor 32 and, thus, controls the charging currentsupplied to upper pulley 6 to charge the downward travel of the belt 2.

The invention has been shown and described as employing inductioncharging of the belt. However, it will be apparent that the invention isequally useful with other types of charging, such as spray charging.Moreover, where the specification refers to putting positive charges onthe belt, this is intended to include removal of negative charges fromthe belt.

In addition, numerous other variations and modifications may obviouslybe made without departing from the invention. Accordingly, it should beclearly understood that those forms of the invention described above andshown in the figures of the accompanying drawings are illustrative onlyand are not intended to limit the scope of the invention.

We claim:

1. A belt-type electrostatic generator comprising a moving belt capableof carrying electrical charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing means atthe other of said pulleys for removing said first charges from saidbelt, a high voltage terminal, means for applying charges removed fromsaid belt to said high voltage terminal, a load circuit connected tosaid high voltage terminal, voltage dropping means included in said loadcircuit, second charging means located at said other pulley and spacedin the direction of belt movement from said first charge removing means,said second charging means utilizing the voltage developed across saidvoltage dropping means to charge the other travel of said belt withsecond electrical charges of second polarity, and second charge removingmeans at said one pulley for removing said second charges from saidbelt.

2. A belt-type electrostatic generator comprising a moving belt capableof carrying electrical charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing means atthe other of said pulleys for removing said first charges from saidbelt, a high voltage terminal, means for applying charges removed fromsaid belt to said high voltage terminal, a load circuit connected tosaid high voltage terminal, corona discharge means included in said loadcircuit, second charging means located at said other pulley and spacedin the direction of belt movement from said first charge removing means,said second charging means utilizing the voltage developed across saidcorona discharge means to charge the other travel of said belt withsecond electrical charges of second polarity, and second charge removingmeans at said one pulley for removing said second charges from saidbelt.

3. A belt-type electrostatic generator comprising a moving belt capableof carrying electrical charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing meansadjacent the other of said pulleys for removing said first charges fromsaid belt, a high voltage terminal, means for applying charges removedfrom said belt to said high voltage terminal, a voltage dropping deviceconnected to said high voltage terminal, a reference potential, a loadcircuit connected in series between said voltage dropping device andsaid reference potential, means connecting said other pulley to the lowvoltage side of said voltage dropping device, an induction plate mountedadjacent said other pulley outside of said belt, and means connectingsaid induction plate to said high voltage terminal to charge the othertravel of said belt with second electrical charges of second polarity,and

second charge removing means at said one pulley for removing said secondcharges from said belt.

4. A belt-type electrostatic generator comprising a moving belt capableof carrying electrical charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing meansadjacent the other of said pulleys for removing said first charges fromsaid belt, a high voltage terminal, means for applying charges removedfrom said belt to said high voltage terminal, a voltage dropping deviceconnected to said high voltage terminal, a reference potential, a loadcircuit connected in series between said voltage dropping device andsaid reference potential, variable resistance means connecting saidother pulley to the low voltage side of said voltage dropping device, aninduction plate mounted adjacent said other pulleys outside said belt,and means connecting said induction plate to said high voltage terminalto charge the other travel of said belt with second electrical chargesof second polarity, and second charge removing means at said one pulleyfor removing said second charges from said belt.

5. A belt-type electrostatic generator comprising a moving belt formedof electrically insulating material, a pair of spaced pulleys supportedsaid belt for revolution about said pulleys, first charging meanslocated at one of said pulleys for charging one travel of said belt withfirst electrical charges of a first polarity, a high voltage terminal,means connecting the other of said pulleys to said high voltage terminalto transmit said first charges from said belt to said high voltageterminal, a pair of concentric sleeves mounted adjacent one end of saidhigh voltage terminal and electrically insulated from each other andfrom said high voltage terminal, a load connected between said highvoltage terminal and the inner one of said sleeves, a first corona pointmounted on the outer one of said sleeves and forming a first corona gapwith the inner one of said sleeves, a grounded tank encircling saidgenerator, a second corona point mounted on said tank and forming asecond corona gap with the outer one of said sleeves, an idler pulleyengaging said belt at a point spaced from said other pulley in thedirection of belt movement, means connecting said idler pulley to theouter one of said sleeves, an induction plate mounted adjacent saididler pulley, means connecting said induction plate to the inner one ofsaid sleeves to cause said induction plate to induce second electricalcharges of a second polarity on the other travel of said belt, and meansat said one pulley for removing said second charges from said belt.

6. A belt-type electrostatic generator comprising a moving belt capableof carrying electrical charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys, for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing means atthe other of said pulleys for removing said first charges from saidbelt, a high voltage terminal, a gas filled acceleration tube includingan ion source having an anode and a cathode, means connecting the anodeof said ion source to said high voltage terminal, means connecting saidother pulley to the cathode of said ion source, means for controllingthe gas pressure in said acceleration tube to control the voltage dropacross said ion source, an induction plate mounted adjacent said otherpulley outside said belt, means connecting said induction plate to saidhigh voltage terminal for charging said belt with second electricalcharges of second polarity, and second charge removing means at said onepulley for removing said second charges from said belt.

7. A belt-type electrostatic generator comprising a moving belt capableof carrying electric charge, a pair of spaced pulleys supporting saidbelt for revolution about said pulleys, first charging means located atone of said pulleys for charging one travel of said belt with firstelectrical charges of a first polarity, first charge removing meansadjacent the other of said pulleys for removing said first charges fromsaid belt, a high voltage terminal, means for applying charges removedfrom said belt to said high voltage terminal, an acceleration tubeincluding an ion source having an anode and a cathode, a voltagedropping device connected in series between said anode and said highvoltage terminal, second charging means located at said other pulley andspaced in the direction of belt movement from said first charge removingmeans,

said second charging means utilizing the voltage developed across saidvoltage dropping device to charge the other travel of said belt withsecond electrical charges of second polarity, and second charge removingmeans at said one pulley for removing said second charges from saidbelt.

References Cited in the file of this patent UNITED STATES PATENTS NygardMay 4, 1954 2,883,606 Gale et al. Apr. 21, 1959 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent Noo 3,024.40? March 6 1962Reuben A. Bergan et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2 line 2, for "bore hole" read borehole column 3, line 51, for"sleves" read sleeves column 4, line 36, for "votlage" read voltagecolumn 6 line 18 for "pulleys" read pulley line 26 for "supported" readsupporting Signed and sealed this 19th day of June 1962.

(SEAL) Atteet:

ERNEST w. SWIDER DAVID L LA D Attesting Officer Commissioner of Patents

